1. Field of the Invention
This invention relates to a reflective display device, and more particularly to a reflective display device that is capable of improving a light efficiency in a reflective liquid crystal display in which a light is obliquely inputted from a peripheral light source or an auxiliary light source.
2. Description of the Related Art
A liquid crystal display (LCD) is a flat panel display device having advantages of small bulk, thin thickness and low power consumption. The LCD has been used as a portable computer such as a notebook personal computer, an office automation equipment and an audio/video machinery, etc. The LCD controls an electric field applied to a liquid crystal material having a dielectric anisotrophy to transmit or shut off a light, thereby displaying a picture or an image. The LCD exploits an external light rather than generating a light by himself unlike display devices such as an electro-luminescence (EL) device, a cathode ray tube (CRT), a light emitting diode (LED) and so on.
The LCD is largely classified into a transmissive type and a reflective type depending on a method of exploiting a light. The transmissive LCD includes a liquid crystal panel having a liquid crystal material injected between two glass substrates, and a back light for supplying a light to the liquid crystal panel. However, the transmissive LCD has not only a difficulty in making a product with a thin thickness and a light weight, but also it has a drawback in which the back light has an excessive power consumption. On the other hand, the reflective LCD includes a reflective liquid crystal display panel 10 that transmit and reflect a natural light and a peripheral light to and from the display screen without a back light as shown in FIG. 1. The reflective liquid crystal panel 10 consists of a liquid crystal panel 2 in which a liquid crystal material is injected between two glass substrates, and a reflector 4 arranged at the rear side of the liquid crystal panel 2 or arranged at the interior of the liquid crystal panel to reflect a light toward the display screen. This reflective LCD does not use the back light, but reflects a natural light or a peripheral light by means of the reflector 4 so as to display a picture or an image. However, since the reflective LCD has a considerably low brightness level at a place where a natural light or a peripheral light is not sufficient, it does not permit an observer to view the displayed image. In order to solve this problem, there has been suggested a reflective LCD exploiting an auxiliary light other than a natural light.
FIG. 2 shows a conventional reflective LCD disclosed in U.S. Pat. No. 5,477,239. Referring to FIG. 2, the conventional reflective LCD includes a display module 24 installed pivotally at a main body 28 and mounted with a reflective liquid crystal panel 22, and auxiliary light sources 26a and 26b of a line light source type installed at the left and right sides of the reflective liquid crystal panel 22, respectively. Each auxiliary light source 26a and 26b is installed on the display module 24 such that they can be opened and closed, and irradiates a light onto the reflective liquid crystal display panel 22 in a state of being exposed to the exterior of the display module 24. As seen from FIG. 3, a film 30 is attached onto an upper glass substrate of the reflective liquid crystal display panel 22. As shown in FIG. 4, this film 30 is provided with a plurality of minute protrusion patterns 30a for turning a light inputted from the auxiliary light sources 26a and 26b into the display screen of the reflective liquid crystal panel 22.
However, in the reflective LCD shown in FIG. 2, since the auxiliary light sources 26a and 26b have to be installed within the display module 24, an effective display area of the reflective liquid crystal display panel 22 is relatively reduced to that extent. To enlarge the effective display area raises a problem of a dimension increase of the display module 24. Also, the reflective LCD has a problem in that an light incidence efficiency becomes low due to a light-intensity difference of a light being incident to the reflective liquid crystal display panel 22 in accordance with a distance difference from the auxiliary light sources 26a and 26b. Furthermore, the conventional reflective LCD has a drawback in that, since the minute protrusion patterns 30a of the film 30 must have different inclination angle and height for each location thereof so that a light can be uniformly incident to the display screen of the reflective liquid crystal display panel 22, they have a difficulty in their design and manufacturing. Also, since the film 30 has plane parts existing between the minute protrusion patterns 30a so that it make no effect to an external peripheral light other than the auxiliary light sources 26a and 26b, it can reflect only a light inputted at a very large incline from the auxiliary light sources 26a and 26b into the reflective liquid crystal display panel 22.
FIG. 5 shows a conventional reflective LCD disclosed in U.S. Pat. No. 5,341,231. Referring to FIG. 5, the conventional reflective LCD includes a light guide 34 applied to the front surface of a reflective liquid crystal display panel 32, and lamps 38a and 38b installed at each side of the light guide 34. The rear side of the light guide 34 applied to the front surface of the reflective liquid crystal display panel 32 is provided with minute protrusion patterns 34a. The minute protrusion patterns 34a refracts a light inputted obliquely via lamps 38a and 38b and a collimator (36a, 36b) in a direction perpendicular to the reflective liquid crystal display panel 32. As a light outputted from the light guide 34 is inputted as perpendicularly as possible to the reflective liquid display panel 32, a reflection from the surface of the liquid crystal display panel 32 is more reduced and a picture brightness is more increased. However, an inclined-direction component of a light outputted from the light guide 34 as shown in FIG. 5 becomes larger than a vertical-direction component thereof as seen from FIG. 6. Thus, a light intensity being incident to the reflective liquid crystal panel 32 from the light guide to make a direct contribution to a brightness of the reflective liquid crystal display panel is only a portion of total light intensity.
Accordingly, it is an object of the present invention to provide a reflective display device that is capable of improving a light efficiency in a reflective liquid crystal display in which a light is obliquely inputted from a peripheral light source or an auxiliary light source.
In order to achieve these and other objects of the invention, a reflective display device according to an embodiment of the present invention includes reflective display means for displaying an image; and an optical medium having an inclined surface for refracting an incident light and refracting a light reflected from the reflective display means such that an obliquely inputted external light is vertically incident to the reflective display means.